A trailer in a tractor-trailer combination is connected to the "fifth wheel" of a tractor by a fifth wheel kingpin. Through continued use, the kingpin will wear resulting in a decreased diameter and a consequent diminishment of the security of the connection between the tractor and the trailer.
One method of restoring the diameter of a fifth wheel kingpin is to build it up by depositing new metal on the surface of the kingpin and subsequently machining the build-up kingpin down to its operational size. Although this could be done by first removing the kingpin from the trailer, in order to minimize downtime, it is preferable to build-up and machine the kingpin back down to operational size without removal from the trailer (i.e., "in situ").
It is an object of the present invention to provide a portable orbital lathe for economical in situ machining of a fifth wheel kingpin.